The present invention relates to monobenzene nitrophenylenediamines having at least one cationic charge delocalized on an unsaturated 5-membered polynitrogenous heterocycle, and comprising at least one cationic group which is chosen from certain aliphatic chains, to their use as direct dyes in dyeing applications for keratinous substances, in particular for human keratinous fibers and especially the hair, to the dyeing compositions comprising them, and to the dyeing processes employing such compositions.
It is known to dye keratinous fibers, and in particular the hair, with dyeing compositions comprising direct dyes, that is to say coloring molecules having an affinity for the fibers. The dyeing process which employs them is a so-called direct dyeing process, wherein the direct dyes are allowed to stand on the fibers and are then rinsed.
The colorings which result therefrom are temporary or semi-permanent colorings, because the nature of the interactions which bind the direct dyes to the keratinous fiber and their desorption from the surface and/or from the core of the fiber are responsible for their weak dyeing power and their poor ability to withstand washing operations or perspiration.
Cationic nitrophenylenediamines have certainly already been described among known direct dyes but their cationic charge is localized on the nitrogen atom of an aliphatic chain or of a mononitrogenous heterocycle. Such nitrophenylenediamines are disclosed, for example, in British Patent No. 1,164,824 and U.S. Pat. No. 4,018,556, the disclosures of which are incorporated by reference herein.
However, in hair dyeing, there is a constant search for direct dyes which exhibit improved characteristics.
It is therefore after a great deal of research directed at this question that the inventors have now just discovered, entirely unexpectedly and surprisingly, novel cationic monobenzene nitrophenylenediamines with at least one cationic charge delocalized over an unsaturated 5-membered polynitrogenous heterocycle and therefore comprising at least one Z cationic group, Z being chosen from quaternized aliphatic chains, aliphatic chains comprising at least one quaternized saturated ring and aliphatic chains comprising at least one quaternized unsaturated ring.
This novel family of dyes exhibits the highly advantageous distinguishing feature of a greater solubility in dyeing media, and these novel dyes produce colors, by direct coloring, which possess a power and a resistance (to the various attacks which hair may be subject to: light, rubbing, bad weather, shampoos or perspiration) which are significantly improved with respect to those of the colors produced with known cationic nitrophenylenediamines of the prior art, the cationic charge of which is localized on the nitrogen atom of an aliphatic chain or of a mononitrogenous heterocycle.
This discovery forms the basis of the present invention.
The subject of the present invention is thus the cationic monobenzene nitrophenylenediamines of following formula (I): 
in which formula,
R1, R2, R3 and R4, which can be identical or different, represent a hydrogen atom; a Z group defined below; a (C1-C6)alkyl radical; a monohydroxy(C1-C6)alkyl radical; a polyhydroxy(C2-C6)alkyl radical; a (C1-C6)alkoxy(C1-C6)alkyl radical; an aryl radical; a benzyl radical; a cyano(C1-C6)alkyl radical; a carbamyl(C1-C6)alkyl radical; an Nxe2x80x94(C1-C6)alkylcarbamyl(C1-C6)alkyl radical; an N,N-di(C1-C6)alkylcarbamyl(C1-C6)alkyl radical; a thiocarbamyl(C1-C6)alkyl radical; a trifluoro-(C1-C6)alkyl radical; a sulpho(C1-C6)alkyl radical; a (C1-C6)alkylcarboxy(C1-C6)alkyl radical; a (C1-C6)alkylsulphinyl(C1-C6)alkyl radical; an aminosulphonyl(C1-C6)alkyl radical; an Nxe2x80x94Z-aminosulphonyl(C1-C6)alkyl radical; an Nxe2x80x94(C1-C6)alkylaminosulphonyl(C1-C6)alkyl radical; an N,N-di(C1-C6)alkylaminosulphonyl(C1-C6)alkyl radical; a (C1-C6)alkylcarbonyl(C1-C6)alkyl radical; an amino(C1-C6)alkyl radical, the alkyl of which is unsubstituted or substituted by one or more hydroxyl radicals; or an amino(C1-C6)alkyl radical, the alkyl of which is unsubstituted or substituted by one or more hydroxyl radicals and the amine of which is substituted by one or two identical or different radicals which may together form, with the nitrogen atom to which they are attached, a carbonaceous 5- or 6-membered ring or a 5- or 6-membered ring comprising one or more heteroatoms, or which are chosen from alkyl, monohydroxy(C1-C6)alkyl, polyhydroxy(C2-C6)alkyl, (C1-C6)alkylcarbonyl, carbamyl, Nxe2x80x94(C1-C6)alkylcarbamyl or N,N-di(C1-C6)alkylcarbamyl, (C1-C6)alkylsulphonyl, formyl, trifluoro(C1-C6)alkylcarbonyl, (C1-C6)alkylcarboxyl or thiocarbamyl radicals, or from a Z group defined below;
R5 and R6, which can be identical or different, represent a hydrogen atom; a halogen atom; a Z group defined below; a (C1-C6)alkylcarbonyl radical; an amino(C1-C6)alkylcarbonyl radical; an Nxe2x80x94Z-amino(C1-C6)alkylcarbonyl radical; an Nxe2x80x94(C1-C6)alkylamino(C1-C6)alkylcarbonyl radical; an N,N-di(C1-C6)alkylamino(C1-C6)alkylcarbonyl radical; an amino(C1-C6)alkylcarbonyl(C1-C6)alkyl radical; an Nxe2x80x94Z-amino(C1-C6)alkylcarbonyl(C1-C8)alkyl radical; an Nxe2x80x94(C1-C6)alkylamino(C1-C6)alkylcarbonyl(C1-C6)alkyl radical; an N,N-di(C1-C6)alkylamino(C1-C6)alkylcarbonyl(C1-C6)alkyl radical; a carboxyl radical; a (C1-C6)alkylcarboxyl radical; a (C1-C6)alkylsulphonyl radical; an aminosulphonyl radical; an Nxe2x80x94Z-aminosulphonyl radical; an Nxe2x80x94(C1-C6)alkylaminosulphonyl radical; an N,N-di(C1-C6)alkylaminosulphonyl radical; an aminosulphonyl(C1-C6)alkyl radical; an Nxe2x80x94Z-aminosulphonyl(C1-C6)alkyl radical; an Nxe2x80x94(C1-C6)alkylaminosulphonyl(C1-C6)alkyl radical; an N,N-di(C1-C6)alkylaminosulphonyl(C1-C6)alkyl radical; a carbamyl radical; an Nxe2x80x94(C1-C6)alkylcarbamyl radical; an N,N-di(C1-C6)alkylcarbamyl radical; a carbamyl(C1-C6)alkyl radical; an Nxe2x80x94(C1-C6)alkylcarbamyl(C1-C6)alkyl radical; an N,N-di(C1-C6)alkylcarbamyl(C1-C6)alkyl radical; a (C1-C6)alkyl radical; a monohydroxy(C1-C6)alkyl radical; a polyhydroxy(C2-C6)alkyl radical; a (C1-C6)alkoxy(C1-C6)alkyl radical; a trifluoro(C1-C6)alkyl radical; a cyano radical; an OR7 or xe2x80x94SR7 group defined below; or an amino(C1-C6)alkyl radical, the alkyl of which is unsubstituted or substituted by one or more hydroxyl radicals and the amine of which is unsubstituted or substituted by one or two identical or different radicals which may together form, with the nitrogen atom to which they are attached, a carbonaceous 5- or 6-membered ring or a 5- or 6-membered ring comprising one or more heteroatoms, or which are chosen from (C1-C6)alkyl, monohydroxy(C1-C6)alkyl, polyhydroxy(C2-C6)alkyl, (C1-C6)alkylcarbonyl, carbamyl, Nxe2x80x94(C1-C6)alkylcarbamyl or N,N-di(C1-C6)alkylcarbamyl, (C1-C6)alkylsulphonyl, formyl, trifluoro(C1-C6)alkylcarbonyl, (C1-C6)alkylcarboxyl or thiocarbamyl radicals, or from a Z group defined below;
R7 denotes a hydrogen atom; a (C1-C6)alkyl radical; a monohydroxy(C1-C6)alkyl radical; a polyhydroxy(C2-C6)alkyl radical; a Z group; a (C1-C6)alkoxy(C1-C6)alkyl radical; an aryl radical; a benzyl radical; a carboxy(C1-C6)alkyl radical; a (C1-C6)alkylcarboxy(C1-C6)alkyl radical; a cyano(C1-C6)alkyl radical; a carbamyl(C1-C6)alkyl radical; an Nxe2x80x94(C1-C6)alkylcarbamyl(C1-C6)alkyl radical; an N,N-di(C1-C6)alkylcarbamyl(C1-C6)alkyl radical; a trifluoro(C1-C6)alkyl radical; an aminosulphonyl(C1-C6)alkyl radical; an Nxe2x80x94Z-aminosulphonyl(C1-C6)alkyl radical; an Nxe2x80x94(C1-C6)alkylaminosulphonyl(C1-C6)alkyl radical; an N,N-da(C1-C6)alkylaminosulphonyl(C1-C6)alkyl radical; a (C1-C6)alkylsulphinyl(C1-C6)alkyl radical; a (C1-C6)alkylsulphonyl(C1-C6)alkyl radical; a (C1-C6)alkylcarbonyl(C1-C6)alkyl radical; an amino(C1-C6)alkyl radical, the alkyl of which is unsubstituted or substituted by one or more hydroxyl radicals; or an amino(C1-C6)alkyl radical, the alkyl of which is unsubstituted or substituted by one or more hydroxyl radicals and the amine of which is substituted by one or two identical or different radicals which may together form, with the nitrogen atom to which they are attached, a carbonaceous 5- or 6-membered ring or a 5- or 6-membered ring comprising one or more heteroatoms, or which are chosen from (C1-C6)alkyl, monohydroxy(C1-C6)alkyl, polyhydroxy(C2-C6)alkyl, (C1-C6)alkylcarbonyl, formyl, trifluoro(C1-C6)alkylcarbonyl, (C1-C6)alkylcarboxyl, carbamyl, Nxe2x80x94(C1-C6)alkylcarbamyl, N,N-di(C1-C6)alkylcarbamyl, thiocarbamyl or (C1-C6)alkylsulphonyl radicals, or from a Z group defined below;
Z is chosen from the unsaturated cationic groups of following formulae (II) and (III) and the saturated cationic groups of following formula (IV): 
xe2x80x83in which formulae:
D is a linking arm which represents a linear or branched alkyl chain preferably comprising from 1 to 14 carbon atoms which can be interrupted by one or more heteroatoms, such as oxygen, sulphur or nitrogen atoms, and which can be substituted by one or more hydroxyl or (C1-C6)alkoxy radicals and which can carry one or more ketone functional groups;
the E, G, J, L and M vertices, which are identical or different, represent a carbon, oxygen, sulphur or nitrogen atom;
n is an integer ranging from 0 to 4;
m is an integer ranging from 0 to 5;
the R radicals, which are identical or different, represent a second Z group identical to or different from the first Z group; a halogen atom; a hydroxyl radical; a (C1-C6)alkyl radical; a monohydroxy(C1-C6)alkyl radical; a polyhydroxy(C2-C6)alkyl radical; a nitro radical; a cyano radical; a cyano(C1-C6)alkyl radical; a (C1-C6)alkoxy radical; a tri(C1-C6)alkylsilyl(C1-C6)alkyl radical; an amido radical; a formyl radical; a carboxyl radical; a (C1-C6)alkylcarbonyl radical; a thio radical; a thio(C1-C6)alkyl radical; a (C1-C6)alkylthio radical; an amino radical; an amino radical protected by a (C1-C6)alkylcarbonyl, carbamyl or (C1-C6)alkylsulphonyl radical; or an NHRxe2x80x2 or NRxe2x80x2Rxe2x80x2xe2x80x3 group in which Rxe2x80x2 and Rxe2x80x2xe2x80x3, which are identical or different, represent a (C1-C6)alkyl radical, a monohydroxy(C1-C6)alkyl radical or a polyhydroxy(C2-C6)alkyl radical;
R8 represents a (C1-C6)alkyl radical; a monohydroxy(C1-C6)alkyl radical; a polyhydroxy(C2-C6)alkyl radical; a cyano(C1-C6)alkyl radical; a tri(C1-C6)alkylsilyl(C1-C6)alkyl radical; a (C1-C6)alkoxy(C1-C6)alkyl radical; a carbamyl(C1-C6)alkyl radical; a (C1-C6)alkylcarboxy(C1-C6)alkyl radical; a benzyl radical; or a second Z group identical to or different from the first Z group;
R9, R10 and R11, which are identical or different, represent a (C1-C6)alkyl radical; a monohydroxy(C1-C6)alkyl radical; a polyhydroxy(C2-C6)alkyl radical; a (C1-C6)alkoxy-(C1-C6)alkyl radical; a cyano(C1-C6)alkyl radical; an aryl radical; a benzyl radical; an amido(C1-C6)alkyl radical; a tri(C1-C6)alkylsilyl(C1-C6)alkyl radical; or an amino(C1-C6)alkyl radical, the amine of which is protected by a (C1-C6)alkylcarbonyl, carbamyl or (C1-C6)alkylsulphonyl radical; two of the R9, R10 and R11 radicals can also together form, with the nitrogen atom to which they are attached, a saturated carbonaceous 5- or 6-membered ring or a saturated 5- or 6-membered ring which can comprise one or more heteroatoms, such as, for example, a pyrrolidine ring, a piperidine ring, a piperazine ring or a morpholine ring, it being possible for the ring to be unsubstituted or substituted by a halogen atom, a hydroxyl radical, a (C1-C6)alkyl radical, a monohydroxy(C1-C6)alkyl radical, a polyhydroxy(C2-C6)alkyl radical, a nitro radical, a cyano radical, a cyano(C1-C6)alkyl radical, a (C1-C6)alkoxy radical, a tri(C1-C6)alkylsilyl(C1-C6)alkyl radical, an amido radical, a formyl radical, a carboxyl radical, a keto(C1-C6)alkyl radical, a thio radical, a thio(C1-C6)alkyl radical, a (C1-C6)alkylthio radical, an amino radical or an amino radical protected by a (C1-C6)alkylcarbonyl, carbamyl or (C1-C6)alkylsulphonyl radical; one of the R9, R10 and R11 radicals can also represent a second Z group identical to or different from the first Z group;
R12 represents a (C1-C6)alkyl radical; a monohydroxy(C1-C6)alkyl radical; a polyhydroxy(C2-C6)alkyl radical; an aryl radical; a benzyl radical; an amino(C1-C6)alkyl radical; an amino(C1-C6)alkyl radical, the amine of which is protected by a (C1-C6)alkylcarbonyl, carbamyl or (C1-C6)alkylsulphonyl radical; a carboxy(C1-C6)alkyl radical; a cyano(C1-C6)alkyl radical; a carbamyl-(C1-C6)alkyl radical; a trifluoro(C1-C6)alkyl radical; a tri(C1-C6)alkylsilyl(C1-C6)alkyl radical; a sulphonamido(C1-C6)alkyl radical; a (C1-C6)alkylcarboxy(C1-C6)alkyl radical; a (C1-C6)alkylsulphinyl(C1-C6)alkyl radical; a (C1-C6)alkylsulphonyl(C1-C6)alkyl radical; a (C1-C6)alkylketo(C1-C6)alkyl radical; an Nxe2x80x94(C1-C6)alkylcarbamyl(C1-C6)alkyl radical; or an Nxe2x80x94(C1-C6)alkylsulphonamido(C1-C6)alkyl radical;
x and y are integers equal to 0 or 1; with the following conditions:
in the unsaturated cationic groups of formula (II):
when x=0, the D linking arm is attached to the nitrogen atom,
when x=1, the D linking arm is attached to one of the E, G, J or L vertices,
y can take the value 1 only:
xe2x80x831) when the E, G, J and L vertices simultaneously represent a carbon atom and when the R8 radical is carried by the nitrogen atom of the unsaturated ring; or else
xe2x80x832) when at least one of the E, G, J and L vertices represents a nitrogen atom to which the R8 radical is attached;
in the unsaturated cationic groups of formula (III):
when x=0, the D linking arm is attached to the nitrogen atom,
when x=1, the D linking arm is attached to one of the E, G, J, L or M vertices,
y can take the value 1 only when at least one of the E, G, J, L and M vertices represents a divalent atom and when the R8 radical is carried by the nitrogen atom of the unsaturated ring;
in the cationic groups of formula (IV):
when y=0, then the D linking arm is attached to the nitrogen atom carrying the R9 to R11 radicals,
when y=1, then two of the R9 to R11 radicals form, jointly with the nitrogen atom to which they are attached, a saturated 5- or 6-membered ring as defined above and the D linking arm is carried by a carbon atom of the saturated ring;
Xxe2x88x92 represents a monovalent or divalent anion and is preferably chosen from a halogen atom, such as chlorine, bromine, fluorine or iodine, a hydroxide, a hydrogen sulphate or a (C1-C6)alkyl sulphate, such as, for example, a methyl sulphate or an ethyl sulphate;
it being understood:
that the number of Z unsaturated cationic groups of formula (II) in which at least one of the E, G, J and L vertices represents a nitrogen atom is at least equal to 1, and
that, when one and only one of the R1 to R4 or R7 radicals denotes a Z group in which the D linking arm represents an alkyl chain comprising a ketone functional group, then the ketone functional group is not directly attached to the nitrogen atom of the NR1R2 or NR3R4 group or to the oxygen atom of the OR7 group when R5 or R6 represents OR7.
The alkyls and alkoxys mentioned above in the formulae (I), (II), (III) and (IV) can be linear or branched.
The compounds of formula (I) can optionally be salified by strong inorganic acids, such as HCl, HBr or H2SO4, or organic acids, such as acetic, tartaric, lactic, citric or succinic acid.
Mention may in particular be made, among the rings of the Z unsaturated groups of above formula (II), by way of example, of the pyrrole, imidazole, pyrazole, oxazole, thiazole and triazole rings.
Mention may in particular be made, among the rings of the Z unsaturated groups of above formula (III), by way of example, of the pyridine, pyrimidine, pyrazine, oxazine and triazine rings.
The compounds of formula (I) are preferably chosen from those of following formulae (I)1 to (I)15: 
i.e., 1-(3-(4-amino-2-chloro-5-nitrophenylamino)propyl)-3-methyl-3H-imidazol-1-ium bromide, 
i.e., 1-(2-(4-amino-2-chloro-5-nitrophenylamino)ethyl)-3-methyl-3H-imidazol-1-ium chloride, 
i.e., 1-(2-(4-amino-2-chloro-5-nitrophenylamino)ethyl)-3-methyl-3H-imidazol-1-ium bromide, 
i.e., 1-(2-(4-amino-2-methyl-5-nitrophenylamino)ethyl)-3-methyl-3H-imidazol-1-ium bromide, 
i.e., 1-(2-(4-amino-2-methylsulphanyl-5-nitrophenylamino)ethyl)-3-methyl-3H-imidazol-1-ium bromide, 
i.e., 1-(2-(4-amino-3-nitrophenylamino)ethyl)-3-methyl-3H-imidazol-1-ium chloride, 
i.e., 3-(3-(4-diethylamino-2-nitrophenylamino)propyl)-1-methyl-3H-imidazol-1-ium methyl sulphate, 
i.e., 3-(3-{4-(bis(2-hydroxyethyl)amino)-2-nitrophenylamino}propyl)-1-methyl-3H-imidazol-1-ium methyl sulphate, 
i.e., 1-methyl-3-(3-(3-methylamino-4-nitrophenylamino)propyl)-3H-imidazol-l1-ium methyl sulphate, 
i.e., 3-(3-{2-chloro-5-(3-(3-methyl-3H-imidazol-1-io)propylamino)-4-nitrophenylamino}propyl)-1-methyl-3H-imidazol-1-ium di(hydrogen sulphate), 
i.e., 3-(3-{4-chloro-5-(3-(trimethylammonio)propylamino)-2-nitrophenyl-amino}propyl)-1-methyl-3H-imidazol-1-ium di(methyl sulphate), 
i.e., 3-(3-{3-(2-(diethylmethylammonio)ethylamino)-4-nitrophenylamino}propyl)-1-methyl-3H-imidazol-1-ium di(methyl sulphate), 
i.e., 1-(2-(4-amino-2-chloro-5-nitrophenylamino)ethyl)-2-methyl-2H-pyrazol-1-ium bromide, 
i.e., 1-(2-(4-amino-2-methylsulphanyl-5-nitrophenylamino)ethyl)-2-methyl-2H-pyrazol-1-ium bromide, 
i.e., 3-methyl-1-{2-(methyl(4-methylamino-3-nitrophenyl)amino)ethyl}-3H-imidazol-1-ium chloride monohydrate.
The compounds of formula (I) in accordance with the invention can be easily obtained according to methods generally well known in the state of the art for the preparation of quaternized amines, for example:
in one step, by condensation of a nitrophenylenediamine comprising a haloalkyl radical with a compound carrying a tertiary amine radical or by condensation of a nitrophenylenediamine comprising a tertiary amine radical with a compound carrying a haloalkyl radical;
or, in two steps, by condensation of a nitrophenylenediamine comprising a haloalkyl radical with a compound carrying a secondary amine or by condensation of a halogenated nitrophenylenediamine with a (disubstituted amino)alkylamine, followed by quaternization with an alkylating agent.
The quaternization stage is generally, for convenience, the final stage of the synthesis but can take place earlier in the sequence of reactions resulting in the preparation of the compounds of formula (I).
Another subject of the invention is a dyeing composition for keratinous substances comprising, in a medium appropriate for dyeing, an effective amount of at least one cationic monobenzene nitrophenylenediamine of formula (I) described above.
Another subject of the invention is a composition for the direct dyeing of human keratinous fibers, such as the hair, comprising, in a medium appropriate for dyeing, an effective amount of at least one cationic monobenzene nitrophenylenediamine as defined above by the formula (I).
Another subject of the invention is the use of the cationic monobenzene nitrophenylenediamines of formula (I) as direct dyes in or for the preparation of dyeing compositions for keratinous substances, in particular for human keratinous fibers, such as the hair.
However, other characteristics, aspects and advantages of the invention will become even more clearly apparent on reading the description which will follow and various concrete but in no way limiting examples intended to illustrate it.
The cationic monobenzene nitrophenylenediamine(s) of formula (I) in accordance with the invention and/or their addition salts with an acid preferably represent from 0.005 to 12% by weight approximately of the total weight of the dyeing composition and more preferably still from 0.05 to 6% by weight approximately of this weight.
The cationic monobenzene nitrophenylenediamines of formula (I) in accordance with the invention can also be used, in the well-known oxidation dyeing processes using oxidation dyes (oxidation dye precursors and, optionally, couplers), to shade or enrich with highlights the colors obtained with the oxidation dyes.
The dyeing composition according to the invention can also comprise, in order to widen the palette of shades and to obtain varied hues, in addition to the cationic monobenzene nitrophenylenediamines of formula (I), other conventionally used direct dye(s) and in particular nitrobenzene dyes other than the cationic nitrophenylenediamines of formula (I) according to the present invention, such as nitrodiphenylamines, nitrophenol ethers or nitrophenols, nitropyridines, anthraquinone dyes, nitroanilines, mono- or diazo, triarylmethane, azine, acridine and xanthene dyes or metal complex dyes.
The proportion of all these other additional direct dyes can vary from approximately 0.05 to 10% by weight with respect to the total weight of the dyeing composition.
The medium appropriate for dyeing (or vehicle) is generally composed of water or of a mixture of water and of at least one organic solvent, in order to dissolve the compounds which would not be sufficiently soluble in water. Mention may be made, for example, as organic solvent, of lower C1-C4 alkanols, such as ethanol and isopropanol, glycerol, glycols and glycol ethers, such as 2-butoxyethanol, propylene glycol or propylene glycol monomethyl ether, and aromatic alcohols, such as benzyl alcohol or phenoxyethanol, the analogous products and their mixtures.
The solvents can be present in proportions preferably ranging from 1 to 40% by weight with respect to the total weight of the dyeing composition and more preferably still from 5 to 30% by weight approximately.
Fatty amides, such as the mono- and diethanolamides of the acids derived from copra, of lauric acid or of oleic acid, can also be added to the composition according to the invention at concentrations ranging from approximately 0.05 to 10% by weight.
Surface-active agents well known in the state of the art and of anionic, cationic, nonionic, amphoteric or zwifterionic type or their mixtures can also be added to the composition according to the invention, preferably in a proportion ranging from approximately 0.1 to 50% by weight and advantageously from approximately 1 to 20% by weight with respect to the total weight of the composition.
Thickening agents can also be used in a proportion ranging from approximately 0.2 to 5%.
The dyeing composition can, in addition, comprise various conventional adjuvants, such as antioxidizing agents, fragrances, sequestering agents, dispersing agents, hair conditioning agents, preserving agents, opacifying agents and any other adjuvant commonly used in dyeing keratinous substances.
Of course, a person skilled in the art will take care to choose the optional additional compound or compounds mentioned above so that the advantageous properties intrinsically attached to the dyeing composition according to the invention are not, or not substantially, detrimentally affected by the envisaged addition or additions.
The dyeing composition according to the invention can be formulated at acidic, neutral or alkaline pH, it being possible for the pH to vary from 3 to 12 approximately and preferably from 5 to 11 approximately. It can be adjusted to the desired value by means of acidifying or basifying agents or of buffers commonly used in dyeing keratinous substances.
Acidifying agents are conventionally inorganic or organic acids, such as, for example, hydrochloric acid, orthophosphoric acid or sulphuric acid, carboxylic acids such as acetic acid, tartaric acid, citric acid or lactic acid, and sulphonic acids.
Mention may be made, among buffers, of, for example, potassium dihydrogen phosphate/sodium hydroxide.
Mention may be made, among basifying agents, by way of example, of aqueous ammonia, alkaline carbonates, alkanolamines, such as mono-, di- and triethanolamines, and their derivatives, sodium hydroxide, potassium hydroxide and the compounds of formula: 
in which W is a propylene residue optionally substituted by a hydroxyl group or a (C1-C4)alkyl radical and R13, R14, R15 and R16, simultaneously or independently of one another, represent a hydrogen atom or a (C1-C6)alkyl or hydroxy(C1-C6)alkyl radical.
The dyeing composition according to the invention can be provided in various forms, such as in the form of a liquid, cream or gel or in any other form appropriate for carrying out dyeing of keratinous substances and more particularly of human keratinous fibers and especially of the hair. In particular, it can be packaged under pressure in an aerosol can in the presence of a propellent and can form a foam.
Another subject of the present invention is a process for dyeing keratinous fibers, in particular human keratinous fibers, such as the hair, by direct coloring, which comprises the step of allowing a dyeing composition comprising at least one cationic monobenzene nitrophenylenediamine of formula (I) to act on dry or wet keratinous fibers. The composition according to the invention can be used as a leave-in composition, that is to say that, after application of the composition to the fibers, drying is carried out without intermediate rinsing.
In other methods of application, the composition is allowed to act on the fibers for an exposure time varying from 3 to 60 minutes approximately, preferably from 5 to 45 minutes approximately, rinsing is carried out, washing is optionally carried out, rinsing is then again carried out, and drying is carried out.
Concrete examples illustrating the invention will now be given.